Relationship Between Zooplankton Community Characteristics and Environmental Conditions in the Surface Waters of the Western Pacific Ocean During the Winter of 2014

Understanding the effects of environmental heterogeneity on zooplankton communities has been a hot topic for several decades. However, relatively little is known about the responses of zooplankton communities to environmental conditions at large scales from inshore waters to the open ocean. Here, we used the abundance, biovolume, taxa and size spectra of zooplankton collected from the surface waters of the western Pacific Ocean during the winter of 2014 to study the relationship between zooplankton community characteristics and environmental conditions using multiple linear regression (MLR) analysis and redundancy analysis (RDA). According to a hierarchical cluster analysis based on hydrographic conditions, the study area was classified into five water masses. Significant correlations were identified between the limited nutrients and the zooplankton abundance and biovolume from inshore waters to the open ocean. Non-metric multidimensional scaling (NMDS) revealed two distinct zooplankton assemblages. In the northern inshore, Copepoda and Euphausiacea were the dominant zooplankton taxa and in other water masses, Chaetognatha and gelatinous zooplankton were the dominant zooplankton taxa in addition to Copepoda. Our results suggested that, on a large scale from inshore waters to the open ocean in the western Pacific Ocean, the spatial distribution of zooplankton taxa was mainly influenced by environmental conditions, while in the inshore waters, it was due to the top-down effect of the dominant zooplankton taxa. Finally, the slope of the normalized biovolume size spectra (NBSS) was negatively correlated with chlorophyll- a (Chl- a ) concentration and PO 4 3− -P concentration in the inshore waters, which indicated that the higher the trophic level the dominant zooplankton taxa were, the steeper the NBSS slope was.